Cochlear Implant Utilizing Mutliple-Resolution Current Sources and Flexible Data Encoding

ABSTRACT

A programmable cochlear implant system utilizes multiple-resolution current sources and flexible data-encoding scheme for transcutaneous transmission. In certain embodiments, the number of current sources may be equal to or greater than 2, but equal or less than N−1, where N is the number of electrodes. The multi-resolution current source may introduce offset currents to achieve perceptually-based multiple resolutions with high resolution at low amplitudes and low resolution at high amplitudes. The flexible data-encoding scheme may allow arbitrary waveforms in terms of phase polarity, phase duration, pseudo-analog-waveform, while producing high-rate and high-temporal-precision stimulation. In one embodiment, a 2-current-source system may support simultaneous and non-simultaneous stimulation as well as monopolar, bipolar, pseudo-tripolar, and tripolar electrode configurations.

FIELD OF THE INVENTION

The present invention relates to an implanted auditory prosthesis thatutilizes multiple-resolution current sources and a data encoding scheme.

BACKGROUND

Cochlear implants are electronic medical device to help deaf orseverely-hearing-impaired people. They typically consist of an externalsignal processor, a transmission coil, an implantable package with areceiver coil, a hermetically sealed circuit, and an electrode array.More particularly, these systems include a microphone to receive soundsand convert them into corresponding electrical signals. These electricalsignals may then be processed to generate a series of stimulation pulsesthat are delivered to the inner ear using a series of implantedelectrodes. The stimulation of these implanted electrodes allows theimplantee to perceive the corresponding ambient sounds.

A typical cochlear implant includes both an external component and aninternal component. The external component will typically include amicrophone, a speech processor, and a radio-frequency transmitter, whilethe internal component includes an implanted receiver, ahermetically-sealed decoding circuit, and a series of implantedelectrodes. However, there are also numerous other designs currentlyavailable. Regardless of the specific configuration, a basic premise ofall cochlear implant devices is that ambient sounds are detected by themicrophone and a transduced signal representative of this signal is thengenerated. The transduced signal is then processed by a speech processorin accordance with one of several possible strategies.

One of the primary design considerations for cochlear implants is thecurrent source design. To that end, there are two primary types ofcurrent source designs currently in use. The first is to use one currentsource for all N electrodes, while the second approach is to use Ncurrent sources for N electrodes. Some products even use 2N currentsources for N electrodes for more flexibility. Each solution has its ownadvantages and disadvantages. For example, with one current source forall electrodes, the size, complexity, and power consumption of currentstimulator are low. But the stimulation mode is also restricted by theability of one current source. No simultaneous stimulation, currentsteering, or multi-polar stimulation strategies are supported. For N (or2N) current sources for N electrodes, more flexibility and functionalityof stimulation are achieved at the expense of size, complexity, andpower consumption.

Current resolution is an important factor for current source design,especially for low stimulation level. For cochlear implant users, theratio of current variation versus current ΔI/I is more important thanthe current variation ΔI itself. Traditional linear step-size currentsource uses a constant ΔI. Therefore, at low stimulation level where Iis small, ΔI/I is large. To lower ΔI/I, one solution is to increase thenumber of current amplitude bit. However, this results in an increase inthe number of current sources in the internal circuit and lowers thestimulation rate (8-bit requires 256 unit current sources and 10-bitrequires 1024 unit current sources). When the stimulation level is closeto the most comfortable loudness (MCL) and the value I is large, ΔI/I isusually too small and the resolution space is wasted. As such, there isa need for an improved cochlear implant which provides a more balancedsolution for both complexity and functionality.

BRIEF SUMMARY OF THE INVENTION

Disclosed and claimed herein is a programmable cochlear implant thatutilizes multiple current sources and a flexible data-encoding scheme.In one embodiment of the invention, a method for stimulating electrodesimplanted in a human inner ear includes the acts of multiplexing currentsources in accordance with a stimulation mode set using a command frame,and encoding stimulation data for the stimulation of the plurality ofelectrodes in a data frame following the command frame, where thestimulation data include electrode address information, phase polarityinformation and amplitude information. The method further includesgenerating a stimulation pulse based on the stimulation data and usingone or more of the current sources in accordance with the stimulationmode, and delivering the stimulation pulse to the electrodes inaccordance with the stimulation data.

Other aspects, features, and techniques of the invention will beapparent to one skilled in the relevant art in view of the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a cochlear prosthesis inwhich two current sources are utilized;

FIG. 2A is the data encoding format supporting from two current sourcesin accordance with one embodiment;

FIG. 2B is one embodiment of a scheme of self-timing withpulse-width-modulation bit coding;

FIG. 3 depicts stimulation modes supported by the data encoding schemeof one embodiment of the invention;

FIGS. 4A-4C depict embodiments of switch networks for variousstimulation modes;

FIGS. 5A-5F depict embodiments of command and data frames for variousstimulation modes in accordance with the principles of the invention;

FIGS. 6A-6B depict an arbitrary waveform generator according to oneembodiment of the invention;

FIG. 7 illustrates one embodiment of a nonlinear step size currentsource implementation scheme;

FIG. 8 shows one embodiment of a schematic for a reference currentselection and offset current control circuit; and

FIGS. 9A-9C illustrate various continuous-interleaved-sampling strategy(CIS) implementations in accordance with one or more embodiments of theinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Described and claimed herein is a programmable cochlear implant systemutilizing multiple-resolution current sources and a flexibledata-encoding scheme. In one embodiment, the system can supportsimultaneous and non-simultaneous stimulation as well as monopolar,bipolar, pseudo-tripolar, and tripolar electrode configurations.

One aspect of the invention is a cochlear implant having 2 to N−1current sources for N electrodes. In one embodiment, the number ofamplitude bits are balanced with the current resolution at a lowstimulation level. By introducing an offset current circuit consistingof three current sources whose states are controlled by 2-bit rangeinformation, a four-range current source may be implemented with fourdifferent current resolutions of I, 2I, 4I, and 8I, where I is theminimum reference current. Compared with traditional single rangecurrent source, this embodiment improves current resolution by 4 timesat low stimulation level, according to one embodiment. In anotherembodiment, the invention provides high resolution by not overlappingresolution space among different ranges.

Another aspect of the invention is a highly-flexible data encodingscheme to support the aforementioned design of 2 to N−1 current sources.The information for each current source may be modularized andconveniently added or removed from a data frame. With each module, thephase polarity, amplitude, stimulating electrode, and phase duration ofelectrical stimulation can be individually set for each current source.Therefore, flexible stimulation modes, stimulation strategies, arbitrarypulse polarity, arbitrary stimulation waveforms, flexible pulse durationand inter-phase gap may all be supported. In one embodiment, the rangeof pulse widths may be from 1 μs to 1024 μs. Similarly, the range ofinter-phase gap may be from 0 μs to 31 μs. In one embodiment, theresolution for both may be essentially 1 μs. Finally, a high-ratestimulation mode is supported by a special command specifying only onepulse duration, producing a 31-kHz overall stimulation rate with 1current source and a 62-kHz rate with 2 current sources.

The timing control for implanted circuit may be an important factor forthe normal operation of a current stimulator. While one solution hasbeen to add a local timer in the implanted circuit, this tends toincrease the power consumption and lower the reliability of the circuit.Moreover, any minor defect of the timer will cause unpredictable errorin the internal circuit and current stimulator. Also, it is verydifficult to synchronize the timing between external timer and internaltimer. To achieve a reliable synchronization between the two timers,usually a phase lock loop (PLL) circuit is required in the implantedcircuit, which itself is complicated and power hungry. Thus, anotheraspect of the invention is to provide timing from outside such that notimer or PLL circuit is required inside. As will be described in moredetail below, with a careful design of bit coding which enables signallevel changes at the beginning of each data bit, this data encodingscheme can provide timing information to the implanted circuit, inaddition to providing power and data.

Referring first to FIG. 1, depicted is one embodiment of a cochlearprosthesis 100 configured to implement one or more embodiments of theinvention. As shown, the cochlear prosthesis 100 includes acool/transformer 105 coupled to a rectifier/LPF power supply 110 and aprocessing circuit 115. In one embodiment, the power supply 110 isitself electrically coupled to the processing circuit 115, as shown inFIG. 1.

While in the embodiment of FIG. 1 processing circuit 115 includes twocurrent sources 120 ₁ and 120 ₂, it should equally be appreciated thatadditional current sources may similarly be included. As shown, currentsources 120 ₁ and 120 ₂, are each coupled to multiplexers 125 ₁ and 125₂, respectively. In turn, multiplexers 125 ₁ and 125 ₂ may providecurrent signals to a plurality of electrodes 130, in accordance with aselected stimulation mode. While 24 electrodes are depicted in FIG. 1,it should equally be appreciated that more or fewer electrodes may beincluded with the cochlear prosthesis 100 of FIG. 1.

Processing circuit 115 is further depicted as including a data decoder135 for decoding the incoming data, and mode detector 140 for detectingthe mode of the incoming data. Once the data is decoded and the modedetected, the data distributor 145 may use this information to controlthe current sources 120 ₁ and 120 ₂, timing control 150 and electrodeselector 155, as shown in FIG. 1. As shown, the timing control 150 andelectrode selector may be used to selectively stimulate one or more ofthe plurality of electrodes 130 using one or both of the current sources120 ₁ and 120 ₂. The processing circuit 115 may further comprise avoltage sampler 160 and backward data coder 165 for transmittinginformation regarding electrode impedance, electrical field potentials,current flow through the internal receiving coil, data decoding status,and evoked neural activities. It should be understood that, with theexception of the plurality of electrodes 130, the other components ofthe cochlear prosthesis 100 may comprise an external portion, meaningthat such components may not be implanted under the skin or residingwithin the inner ear.

With the 2-current-source configuration of FIG. 1 and a highly-flexibledata encoding scheme as described herein, a large variety of stimulationmodes and strategies may be implemented. If only one current source wereused, only standard mono-polar or bipolar CIS stimulation pulses can begenerated. By using two current sources simultaneously (e.g., currentsources 120 ₁ and 120 ₂), traditional non-overlapping CIS, as well asoverlapping CIS (virtual channel) and even alternating monophasic CISare enabled.

Referring now to FIG. 2A, depicted is one embodiment of a data frame 200comprised of a total of 50 bits. In the depicted embodiment, theindividual bits include:

Bits 1-2: 2 bits, start of a data frame.

Bits 3-7: 5 bits electrode info for current source 1, named Pulse1.

Bit 8: 1 bit sign info of first phase of Pulse1, “0” negative, “1”positive.

Bit 9: 1 bit sign info of second phase of Pulse1 “0” negative, “1”positive.

Bits 10-17: 8 bits amplitude info of Pulse1.

Bit 18: 1 bit parity check for Pulse1 info, bits 3-17.

Bits 19-23: 5 bits electrode info for next pulse of current source 2,named Pulse2.

Bit 24: 1 bit sign info of first phase of Pulse2, “0” negative, “1”positive.

Bit 25: 1 bit sign info of second phase of Pulse2, “0” negative, “1”positive.

Bits 26-33: 8 bits amplitude info of Pulse2.

Bit 34: 1 bit parity check for Pulse2 info, bits 19-33.

Bits 35-44: 10 bits phase width.

Bits 45-49: 5 bits inter-phase gap.

Bit 50: 1 bit parity check for phase info, bits 35-49.

The bit coding of the proposed data encoding scheme may be used toprovide timing control for internal pulse generation. In this way, theimplanted circuit may not require a local timer. After electrode andamplitude information are provided in the beginning of a data frame, theremaining bits in a data frame (e.g., data frame 200) provide pulsewidth and inter-phase gap information and may also act as clock signalfor the timing control of current pulse. Phase extending bits can beadded after a data frame to generate long phase duration pulses. Thestart and end of each phase of a pulse may be synchronized by the onsetof bits in a data frame. In one embodiment, each bit may include of 10to 15 RF cycles to provide cycle error tolerance. It should beappreciated that the proposed timing control may make the implantedcircuit more reliable and easier to implement.

As previously mentioned, one embodiment of the coding scheme may supportflexible 2 to N−1 current sources for N electrodes. For each currentsource, one embodiment of the coding scheme has 16 bits in date frame200 corresponding to it, including 5-bit electrode address information,2-bit phase polarity information and 8-bit pulse amplitude information,and 1 parity check bit. In this fashion, multiplexing of 2 or morecurrent sources to achieve monopolar, bipolar, and pseudo-tripolarstimulation modes is enabled. The pseudo-tripolar refers to apically orbasally applied negative current to sharpen the electric field. A truetripolar will sharpen the field from both sides. In certain embodiments,alternating mono-phasic stimulus may result in the power consumptionbeing at least as good as regular bipolar stimulation. In addition, with3 or more current sources true tripolar stimulation may be provided.

It should further be appreciated that multiplexing 2 or more currentsources may achieve both simultaneous and non-simultaneous virtualchannels. To that end, in one embodiment the total number of virtualchannel may be at least N+(N−1), where N is the number of electrodes.

In certain embodiments, a pulse (e.g., Pulse1, Pulse2) always starts andfinishes within one data frame. After electrode, amplitude and phasepolarity information are provided, the width and phase gap bits in adata frame may act as a clock signal for the timing control of presentpulse. The start and end of each phase of a pulse may be synchronized bythe onset of bits in a data frame.

Referring now to FIG. 2B, depicted is one embodiment of a bit codingscheme 210 in which pulse width modulation with 15 radio frequency (RF)cycles are used. In one embodiment a “0” bit has 5 on-cycles and 10off-cycles. Similarly, a “1” bit may have 10 on-cycles and 5 off-cycles.Redundant cycles may be included to tolerate up to 2-cycle errors. Byway of example, Table 1 below shows one embodiment of a decoding scheme:

TABLE 1 Decoding Scheme Error on-cycle ≦ 2 “0” 3 ≦ on-cycle ≦ 7 “1” 8 ≦on-cycle ≦ 12 Error on-cycle ≧ 13

In one embodiment, each bit must start with an on-cycle and end with anoff-cycle. In this way, the start of a bit may be associated with arising edge, which can be used as a clock signal to trigger other eventsin the implanted circuit.

In one embodiment, the flexible coding scheme of the invention mayprovide a high temporal resolution, with the shortest pulse durationbeing set to 8 μs and a temporal resolution set to one period of databit (0.5 μs). This high temporal resolution may also allow accurateencoding of fundamental frequency (F0) and frequency modulated (FM)information.

Stimulation Mode

Referring now to FIG. 3. depicted are at least some of the stimulationmodes supported by the data encoding scheme of one embodiment of theinvention. In particular, an internal electrode configuration 310 for amonopolar stimulation mode is shown. In addition, FIG. 3 further depictsan internal electrode configuration 320 for a bipolar stimulation mode,an internal electrode configuration 330 for a pseudo-tripolarstimulation mode, and an internal electrode configuration 340 for atripolar stimulation mode. In this fashion, one embodiment of theinvention may provide a flexible encoding scheme for a variety ofstimulation modes.

Referring now to FIGS. 4A-4C, depicted are exemplary switch networks forvarious stimulation modes, in accordance with the principles of theinvention. As shown, a flexible coding scheme of the invention may allowhigh power and coding efficiency, while providing arbitrary waveformoutputs, including alternating or consecutive monophasic pulses forpower and electric stimulation efficiency. To that end, FIG. 4A depictsa switching network 400 comprising of a first current source 410 and asecond current source 420, electrically connected to a plurality ofelectrodes 430 ₁-430 _(n). As will be understood by one in the art, whenone or more of the switches of switch network 400 are closed, a voltageV_(DD) may be provided to stimulate one or more of the plurality ofelectrodes 430 ₁-430 _(n).

FIG. 4B depicts the switching network 400 in which bipolar stimulationof the plurality of electrodes 430 ₁-430 _(n) is being implemented usingthe first current source 410 and the second current source 420. Asshown, switches 435, 440, 445 and 450 have been closed in order toimplement bipolar stimulation. It should of course be understood thatnumerous other switching arrangements may be used in accordance with theinvention.

Referring now to FIG. 4C, depicted is the switching network 400implementing tripolar stimulation of the plurality of electrodes 430₁-430 _(n) using the first current source 410 and the second currentsource 420. As shown, in addition to having switches 435 and 440 closed,switches 455 and 460 are also closed. In addition, switches 445 and 450have been opened in order to implement the tripolar stimulation scheme.As with the embodiment of FIG. 4B, it should of course be understoodthat numerous other switching arrangements may be used in accordancewith the invention.

In certain embodiments, the stimulation mode may be set in the commandframe not in the data frame. As previously mentioned, four of thepossible stimulation modes include bipolar, monopolar, pseudo-tripolarand tripolar.

Bipolar stimulation can be implemented by either using one currentsource multiplexing between different electrodes, or by using twocurrent sources in a monopolar mode. By way of example, FIG. 5A depictsone embodiment of a command frame 500 for the bipolar mode at a firstelectrode (e.g., one of electrodes 130) using a first current source(e.g., current source 120 ₁). Similarly, an exemplary data frame 510 isalso depicted in FIG. 5A.

By way of providing another example of bipolar stimulation, FIG. 5Bdepicts another exemplary command frame 520 and corresponding data frame530 for a first electrode, but in this case using two current sources(e.g., current source 120 ₁ and current source 120 ₂). In oneembodiment, the polarity of the two current sources may be opposite inorder to cancel out the electrode field outside of the two electrodes.

With respect to a monopolar stimulation mode, one embodiment of acommand frame 540 and data frame 550 using one current source aredepicted in FIG. 5C.

In the case of a Pseudo-tripolar stimulation mode, one embodiment of acommand frame 560 and data frame 570 using one current source aredepicted in FIG. 5D. In the pseudo-tripolar mode of FIG. 5D, only onecurrent source may be used and the returning two electrodes may begrounded.

An exemplary command frame 580 and data frame 590 for a tripolarstimulation mode are shown in FIG. 5E. As shown, two current sources areused, and each returning electrode drain is half of the total current.

Finally, a special high-rate stimulation mode can be achieved using ahigh-rate mode command using a high rate data frame 595, as shown in theembodiment of FIG. 5F. Information regarding stimulation mode, pulseduration, gap duration, and current source may be transmitted beforestimulation. In certain embodiments, only information regardingelectrode, pulse polarity, and amplitude may be updated for cycle.Stimulation may start as soon as all 18 bits are transferred anddecoded. The overall stimulation rate can be as high as 31-kHz with 1current source and 62-kHz with 2 current sources.

Arbitrary Waveform Generation

Referring now to FIGS. 6A-6B, depicted is an arbitrary waveform 600generated using a flexible phase polarity, in accordance with oneembodiment of the invention. As shown, each pulse comprises two phasesthereby forming a bi-phasic period. The total charge for one period ofthe sinusoid 610 may be zero, meaning that the total charge is balanced.However, unlike the typical case, the polarity of each of the two phasesof a pulse, such as pulse 620, may be arbitrarily assigned. This mayallow for alternating phase pulses (negative-positive,positive-negative) and monolithic phase pulses (negative-negative,positive-positive), unlike prior art embodiments. This feature may beespecially useful to generate pseudo-analog-waveform stimulations, wherethe biphasic pulses are not charge balanced for each individual pulse,but the accumulated long term charge is balanced over the entiresinusoid 610, as shown in FIG. 6A. In one embodiment, this is enabledusing the previously-described two polarity bits for the two individualphases. While it should be appreciated that the sinusoid 610 may belonger or shorter, in one embodiment the sinusoid 610 may beapproximately 100 μs, while the bi-phasic period 630 may beapproximately 50 μs. Obviously, different values may assigned to each ofthe sinusoid 610 and/or period 630.

Referring now to FIG. 6B, depicted is an enlarged view of the bi-phasicperiod 620 of FIG. 6A. As shown, period 620 is comprised of a firstphase 640 and a second phase 650 each having the same polarity, and thusthe same charge over the entire period 630. The next period can beprogrammed to have two pulses with the same amplitude but the oppositepolarity. In certain embodiments, this flexible coding may be used toproduce mono-phasic or tri-phasic waveforms, which have the advantage oflower stimulation thresholds and possibly more focused electrical fieldsthan biphasic waveform. Longer battery life and possibly betterperformance can be achieved.

Strategy Implementation

In the practice of programmable current source design, there has beentwo general approaches. The first approach, which is now largelyobsolete, is to control the gate-source voltage to get variabledrain-source current. This method, used by first generation cochlearimplant products, required that each current source be calibrated due tothe fact that the nonlinear V_(GS)−I_(DS) relationship has a largevariation among transistors.

The second approach for current source design is to use a linearcombination of fixed value current sources to get a desired currentvalue. Usually, a group of high precision fixed value currents is usedas reference currents to generate output current values by currentmirroring. The majority of current cochlear implant products use thistype of current source.

For this type of current sources, to achieve a higher stimulatingaccuracy, a smaller step size ΔI of current increment is required, undera given current range [I_(min), I_(max)]. Thus, more current amplitudebits B are needed to get a smaller step size, as shown below:

${\Delta \; I} = \frac{I_{\max} - I_{\min}}{2^{B}}$

However, more amplitude bits B usually means more unit current sources.For example, B=8 requires 255 unit current sources, and B=10 requires1023 unit current sources. For an integrated circuit implementation, itis undesirable to have so many current sources, since more chip space isrequired causing a parasitic effect.

Current Source Implementation

Consider the example of B=8, I_(min)=0, I_(max)=2 mA, where there are256 current levels with a step size of 8 μA. For small stimulations nearthreshold level T, this step size may be too large such that the actualT level might fall between two current levels. For large stimulationsnear the MCL, this step size may be too small such that differentcurrent levels make no difference to patients, thus wasting limitedcurrent levels. Thus, it may be desirable to use a small step size forsmall currents to get accurate T levels, and a large step size for largecurrents for adequate sensational variation.

One embodiment of a current source control scheme 700 in accordance withthe principles of the invention is depicted in FIG. 7. In oneembodiment, the current control scheme 700 supports nonlinear step-sizesfor different current resolutions 710 ₁-710 _(n), of I, 2I, 4I, 8I, 16Iand 32I, for example, where I is the minimum reference current. In oneembodiment, the amplitude may be encoded with a 6-bit value and therange with a 2-bit value, as described above with reference to FIG. 2.In one embodiment, an offset current circuit may be introduced. By wayof a non-limiting example, the scheme 700 includes current sources 720₁-720 _(n) usable to provide an offset current, and whose states may becontrolled by the 2-bit range information.

Referring now to FIG. 8, depicted is one embodiment of a control circuit800 for reference current and offset current selection. In particular,reference current selector 810 decodes the 2-bit range to select one offour possible reference currents, (i.e., 2 μA, 4 μA, 8 μA and 16 μA).This information may then be used to control the offset current source820, which in one embodiment is based on the selection of currentsources 720 ₁-720 _(n) from FIG. 7. In addition, the current selector810 may further be configured to use the 6-bit amplitude information tocontrol a 6-bit current digital-to-analog converter (DAC) 830. In oneembodiment, the 6-bit DAC and the offset current source may use the samereference current I, in which case only one reference current generatormay be needed. The following Table 2 depicts the exemplar bit controlledvalues for the control circuit 800:

TABLE 2 Exemplary Bit Controlled Current Values Ref- Range erenceMinimum Bits Current Offset Current Current Maximum Current 00 2 μA (0 +0 + 0)*2 =  0 μA 0 + (2⁶ − 1)*2 = 0 μA 126 μA 01 4 μA (32 + 0 + 0)*4 =128 μA 128 + (2⁶ − 1)*4 = 128 μA 380 μA 10 8 μA (32 + 16 + 0)*8 = 384 μA384 + (2⁶ − 1)*8 = 384 μA 888 μA 11 16 μA  (32 + 16 + 8)*16 = 896 μA896 + (2⁶ − 1)*16 = 896 μA 1904 μA

Table 2 above illustrates that for relatively small currents (e.g.,0-126 μA) the step size is 2 μA. For larger currents (896 μA-1904 μA),the step size is shown as being 16 μA. In the depicted embodiment, thecurrent source uses 8 amplitude bits and a 6-bit DAC to achieve aminimal step size of a 10-bit DAC. Compared with 8-bit DAC, the 6-bitDAC uses 53% less unit current sources, and when compared with a 10-bitDAC, the 6-bit DAC uses 88% less unit current sources.

In certain embodiments, 8-bit 256 level nonlinear step size amplitudecontrol may provide one or more of the following features:

-   -   Current precision improved: from 8 μA to 2 μA.    -   Same 8 amplitude bits, rather than 10 bits.    -   Uses 6-bit DAC rather than 10-bit DAC.    -   No command frame needed to set range.    -   Total number of unit current sources decreases from 255 (8-bit        DAC) or 1023 (10-bit DAC) to 119.

FIGS. 9A-9C depict various embodiments of CIS strategies in accordancewith certain embodiments of the invention. In FIG. 9A, for example, amonopolar non-overlapping CIS strategy 900 is depicted. As shown,following command frame 905, data frames 910 are received for each of 24possible channels for a two current source embodiment. In oneembodiment, the data frame 910 may be configured in accordance with theembodiment of FIG. 2. In addition, each of the 24 possible channels maycorrespond to an individual electrode to be stimulated (e.g., electrodes130 of FIG. 1).

Continuing to refer to FIG. 9A, the depicted Chn1 data frame is decodedto produce the corresponding pulse for Chn1 after delay 915 using eitherthe first current source (cs1) or the second current source (cs2).

Similarly, the Chn2 data frame is decoded to produce the correspondingpulse for Chn2, as shown in FIG. 9A. It should be noted that the pulsesfor each of Chn1-Chn24 do not overlap since FIG. 9A corresponds to oneembodiment of a monopolar non-overlapping CIS strategy. Moreover, eachpulse of FIG. 9A further includes an amplitude encoded into thecorresponding data frame, as described above, and may be generated usingeither current source.

FIG. 9B depicts one embodiment of an overlapping CIS strategy 925. Aswith the embodiment of FIG. 9A, a command frame 930 precedes data frames935 for each of 24 possible channels 940, where each channel maycorrespond to an individual electrode to be stimulated (e.g., electrodes130 of FIG. 1). However, unlike the non-overlapping CIS strategy 900,each data frames 935 of the overlapping CIS strategy 935 may includestimulation data for two channels—e.g., Chn1 and Chn13, Chn2 and Chn14,Chn3 and Chn15, etc. Thus, the depicted Chn1,13 data frame may bedecoded to produce the pulse for Chn1 using cs1, as well as the pulsefor Chn13 using cs2. In addition, these pulses may overlap, as shown inFIG. 9B. As with the embodiment of FIG. 9A, the embodiment of 9Bincludes delay 945 which is a result of the decoding process.

FIG. 9C illustrates another embodiment of a CIS strategy 950 in whichtwo current sources are multiplexed to achieve simultaneous andnon-simultaneous virtual channels. In one embodiment, the total numberof virtual channels can be at least N+(N−1), where N equals the numberof electrodes. In another embodiment, more virtual channels are possibleif the amplitudes between two adjacent channels are manipulated.

While the invention has been described in connection with variousembodiments, it should be understood that the invention is capable offurther modifications. This application is intended to cover anyvariations, uses or adaptation of the invention following, in general,the principles of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

1-28. (canceled)
 29. A method for stimulating a plurality of electrodesimplanted in a human inner ear comprising: multiplexing a plurality ofcurrent sources in accordance with a stimulation mode set using acommand frame, wherein the plurality of current sources includes lessthen N current sources, where N is the number of electrodes in saidplurality of electrodes; encoding stimulation data for the stimulationof the plurality of electrodes in a data frame following the commandframe, wherein the stimulation data includes electrode addressinformation, phase polarity information and amplitude information;generating a stimulation pulse based on said stimulation data and usingone or more of the plurality of current sources in accordance with thestimulation mode, wherein at least one of the plurality of currentsources is configured to produce a multi-resolution current based on areference current; and delivering the stimulation pulse to one or moreof the plurality of electrodes in accordance with the stimulation data.30. The method of claim 29, wherein encoding comprises encodingstimulation data for two or more of the plurality of electrodes into asingle data frame.
 31. The method of claim 29, wherein the stimulationpulse begins and ends within a data frame, and wherein the stimulationdata in the data frame further includes pulse width and inter-phase gapinformation.
 32. The method of claim 31, wherein generating thestimulation pulse comprises generating the stimulation pulse using oneor both of the pulse width and inter-phase gap information as a clocksignal for timing control.
 33. The method of claim 29, wherein thestimulation mode is a mode selected from the list consisting of: amonopolar stimulation mode, a bipolar stimulation mode and apseudo-tripolar stimulation mode.
 34. The method of claim 29, whereinmultiplexing comprises multiplexing the plurality of current sources toachieve simultaneous and non-simultaneous virtual channels.
 35. Themethod of claim 29, wherein the stimulation pulse comprises two phases,and wherein the phase polarity information comprises a polarity for eachof the two phases, said polarity being the same for each of the twophases of the stimulation pulse.
 36. The method of claim 35, a secondphase of the stimulation pulse is connected to a first phase of asubsequent pulse to enable tri-phasic stimulation pulses.
 37. The methodof claim 29, wherein encoding the stimulation data comprises encodingthe stimulation data in accordance with acontinuous-interleaved-sampling strategy (CIS), wherein the CIS isselected from the group consisting of: a non-overlapping CIS, ahigh-rate CIS, an overlapping CIS and an alternating monophasic CIS. 38.The method of claim 29, wherein the plurality of current sources furthercomprises a plurality of offset current sources configured to produce amulti-resolution offset current based on the reference current.
 39. Themethod of claim 29, wherein delivering the stimulation pulse comprisestransmitting the stimulation pulse transcutaneously to the plurality ofelectrodes.
 40. A programmable cochlear implant system comprising: aplurality of electrodes implanted in a human inner ear; a plurality ofcurrent sources multiplexed in accordance with a stimulation mode setusing a command frame, wherein the plurality of current sources includesless then N current sources, where N is the number of electrodes in saidplurality of electrodes; and a processing circuit including theplurality of current sources and electrically connected to the pluralityof electrodes, the processing circuit configured to: encode stimulationdata for the stimulation of the plurality of electrodes in a data framefollowing the command frame, wherein the stimulation data includeselectrode address information, phase polarity information and amplitudeinformation, generate a stimulation pulse based on said stimulation dataand using one or more of the plurality of current sources in accordancewith the stimulation mode, wherein at least one of the plurality ofcurrent sources is configured to produce a multi-resolution currentbased on a reference current, and deliver the stimulation pulse to oneor more of the plurality of electrodes in accordance with thestimulation data.
 41. The programmable cochlear implant system of claim40, wherein the processing circuit is further configured to encode thestimulation data for two or more of the plurality of electrodes into asingle data frame.
 42. The programmable cochlear implant system of claim40, wherein the stimulation pulse begins and ends within a data frame,and wherein the stimulation data in the data frame further includespulse width and inter-phase gap information.
 43. The programmablecochlear implant system of claim 42, wherein the processing circuit isfurther configured to generate the stimulation pulse by using one orboth of the pulse width and inter-phase gap information as a clocksignal for timing control.
 44. The programmable cochlear implant systemof claim 40, wherein the stimulation mode is a mode selected from thelist consisting of: a monopolar stimulation mode, a bipolar stimulationmode and a pseudo-tripolar stimulation mode.
 45. The programmablecochlear implant system of claim 40, wherein the plurality of currentsources are multiplexed in accordance with the stimulation mode toachieve simultaneous and non-simultaneous virtual channels.
 46. Theprogrammable cochlear implant system of claim 40, wherein thestimulation pulse comprises two phases, and wherein the phase polarityinformation comprises a polarity for each of the two phases, saidpolarity being the same for each of the two phases of the stimulationpulse.
 47. The programmable cochlear implant system of claim 46, asecond phase of the stimulation pulse is connected to a first phase of asubsequent pulse to enable tri-phasic stimulation pulses.
 48. Theprogrammable cochlear implant system of claim 40, wherein the processingcircuit is further configured to encode the stimulation data inaccordance with a continuous-interleaved-sampling strategy (CIS),wherein the CIS is selected from the group consisting of: anon-overlapping CIS, a high-rate CIS, an overlapping CIS and analternating monophasic CIS.
 49. The programmable cochlear implant systemof claim 40, wherein the plurality of current sources further comprisesa plurality of offset current sources configured to produce amulti-resolution offset current based on the reference current.
 50. Theprogrammable cochlear implant system of claim 40, wherein the processingcircuit is further configured to deliver the stimulation pulse bytransmitting the stimulation pulse transcutaneously to the plurality ofelectrodes.